Pentobarbital augments serotonin-mediated inhibition of cerebellar Purkinje cells.

The ability of pentobarbital to modify the direct effects of iontophoretically ejected serotonin on the firing rates of cerebellar Purkinje cells was examined. Serotonin elicited inhibition, excitation, or a biphasic effect on cerebellar Purkinje cells. With continuous application of iontophoretic pentobarbital at currents found to potentiate GABA-induced inhibition, serotonin-mediated inhibitions were also augmented consistently. When application of serotonin elicited excitation, including a late component of biphasic responses, iontophoretic pentobarbital converted the effect to, primarily, inhibition. Besides increasing the magnitude of serotonin-mediated inhibition, iontophoretic pentobarbital increased the duration of this effect. In another series of experiments using pentobarbital rather than urethan as the anesthetic, serotonin-mediated inhibition was significantly augmented for all ejection currents tested. The GABA antagonists bicuculline, pentylenetetrazole and picrotoxin attenuated pentobarbital augmentation of serotonin-elicited inhibition. We conclude that serotonin-mediated inhibition of Purkinje cells is modifiable by pentobarbital and this effect bears a strong semblance to the actions of barbiturates on GABAergic neurotransmission.